Debug+Checks Testing

I believe things are in a state now where it makes sense for folks to do
periodic testing with --enable-expensive-checks to check for C++ library
misuse. Already the last couple of weeks I've fixed several of these kinds
of bugs that were introduced with new code.

It might make sense to configure at least one of the nightly testers to build
with --enable-expensive-checks and uncover these problems quickly. I'm
having a heck of a time getting through a build-test cycle with a Debug+Checks
compiler because it keeps falling over due to C++ library bugs from new code.

I've got some significant register coalescing changes in the pipeline and I
need to test them thoroughly before I commit. I also need to keep them
current so I need to do frequent updates. This gets hard when updates
break the compiler. These errors are usually trivial to fix as the problem is
obvious from the GLIBCXX_DEBUG error output. It's just a matter of doing
a build and test with --enable-expensive-checks. Most of the problems
happen during llvm-gcc bootstrap so it's not even the case that the full
testsuite needs to be run. Just a few sanity checks.

                                                -Dave

Hi David,

Yep, I've already got a patch for that. It's in testing now and I hope
to commit it tomorrow.

                                    -Dave